In recent years, hitting position adjustment in a main scanning direction using an image forming apparatuses is performed by transferring toners formed on transfer belts to sheets. For example, as shown in FIG. 14, a wedge-shaped correction pattern 200 may include two straight lines, each formed on a transfer belt 31. The straight lines are detected by a sensor 37, and the position of a vertex of the correction pattern 200 is calculated on the basis of a vertex angle and a detected distance of the correction pattern 200. However, it is not possible to accurately calculate the position of the vertex using such a system due to a fluctuation in sub-scanning magnification. For example, when the vertex of the correction pattern 200 is directly detected by the sensor 37, the influence of a fluctuation in the sub-scanning magnification is not prominent. As a result, it may not be possible to detect the vertex of the correction pattern 200 depending on the position of the correction pattern 200.